Most houses in Switzerland are solidly built and generally have a cellar. There is also a high density of private and public protective shelters in Switzerland. Thus, staying indoors or taking cover in a cellar or protective shelter is considered an appropriate protective measure for the general public to take. It is the principal measure to be taken during the passage of a radioactive cloud and offers protection against external irradiation.
External irradiation can occur both as a result of the passage of a radioactive cloud and from deposits in the soil. The expected dose can be reduced by 10 to 50 times through staying indoors or taking cover in a cellar or protective shelter:
- Indoors: protective factor 10
- Cellar/protective shelter: 50
Windows and external doors should remain closed during the passage of the radioactive cloud to limit the entry of radioactivity into houses, cellars or protective shelters. Furthermore, use of artificial ventilation should be avoided as far as possible, since this draws in the outside air. By turning off the ventilation, the inhalation of radioactive particles, which leads to internal irradiation, can be minimised .